In electrical power distribution systems, distribution transformers are used to step down voltage between the high voltage power line and the user. Hence, transformers are present at virtually every distribution point. Transformers are typically mounted above ground on a junction pole, or at ground level on a pad or platform. Increased use of underground power distribution systems has resulted in a corresponding increase in the number of padmounted transformers. The electrical connections between padmounted transformers and the power distribution system must be contained in a manner that will prevent tampering by unauthorized individuals. Typically, this is accomplished by enclosing the transformer connections within a metal cabinet. Hence conventional transformers include a tank, which contains the core and coil assembly immersed in oil, and a cabinet enclosing the front of the tank. Connections for incorporating the transformer into the power distribution system extend through the front plate of the tank and are enclosed by the cabinet. The cabinet typically includes a door hingedly attached to the tank and a sill, or riser, that extends forward from the front plate of the tank and is in contact with the pad. Typically, the tank front plate is attached to the transformer pad. The sill is typically attached to the tank front plate and transformer pad and provides support for the cabinet door when closed as well as supporting a latch and/or lock for retaining the cabinet door in its closed position. The sill further serves to exclude some insects, small animals and moisture from the inside of the cabinet. However, because the sill is bolted to the pad, there is always some clearance between the sill and pad through which insects and moisture can find ingress.
Typically, transformer pads are fabricated from concrete, fiberglass or plastic. Concrete pads can be poured in place, or preassembled off-site. In addition to being heavy and relatively difficult to transport, an additional assembly step is required at the transformer site, wherein the transformer tank and the sill are affixed to the transformer pad. This assembly step takes time and may result in paint damage to the various parts of the transformer enclosure that come in contact with or are being affixed to the transformer pad. Paint damage is undesirable in transformer enclosures, as they are typically exposed to the elements and paint damage can result in increased corrosion.
Similarly, the cabinet sill is conventionally a separately fabricated piece from the rest of the transformer, i.e. the transformer tank and the cabinet door. Therefore, the sill must be affixed to the front plate of the transformer tank, as well as to the transformer pad. This step also requires additional labor and may result in paint damage to the sill itself, the tank or the door.
Transformer pads typically have predominantly planar upper surfaces. Some pads incorporate ridges and raised bosses on the top surface to facilitate location, placement, and attachment of the transformer on the pad and to provide a degree of tamper resistance. Ridges are typically located inside the transformer sill walls. Cabinet doors close over the top of the ridges to prevent the accumulation and containment of potentially corrosive liquids and airborne particles. Placement of the ridges inside the sill walls also provides an obstacle to objects inserted between the walls and pad and intruding into the transformer interior. The degree to which the ridges succeed as a barrier to intrusion is dependent on the flexibility of the inserted object. A flexible object might bend and skate around the ridges.
When installed, transformer pads are typically flush or very close to flush with ground level. Often the pads become buried after installation. The placement of the pad at ground level or below-grade allows the accumulation of chemicals and liquids, which causes corrosion at the base of the transformer enclosure. Ground level corrosion of the sill and tank is frequently accelerated by paint damage caused by yard care tools and equipment.
Recently, pads for transformers, switch boxes, junction boxes and the like have been developed that are lighter and easier to transport. These may be formed of plastic or fiberglass, and may include a foam core or other internal structural members. Although these pads are more easily installed at the pad site than concrete pads, they still require the additional assembly step wherein the cabinet sill is attached to the transformer tank and pad, and the pads still become buried. Hence, it is desired to provide a transformer pad that eliminates some of the assembly steps for a transformer enclosure by reducing the number of parts required. It is further desired to provide a transformer enclosure having enhanced corrosion resistance and increased resistance to tampering. It is further desired to provide a transformer with a pad that is easily transported and installed at the power distribution site.